Residential and commercial heat pump systems are known to employ modified automotive heat exchangers, which are desirable for its proven high heat transfer efficiency, durability, and relatively ease of manufacturability, as heat pump heat exchangers. A conventional automotive heat exchanger typically includes an inlet manifold, an outlet manifold, and a plurality of refrigerant tubes hydraulically connecting the manifolds for refrigerant flow therebetween. The refrigerant tubes utilized are typically flat tubes having a plurality of micro-channels, or ports, for refrigerant flow and are manufactured from extruded aluminum alloy or folded from a sheet of aluminum alloy. Corrugated fins interconnect adjacent refrigerant tubes to increase the available heat transfer area, as well as to increase the structural integrity of the heat exchanger. The core of the heat exchanger is defined by the refrigerant tubes and interconnecting corrugated fins.
Heat pump heat exchangers, also known as heat pump coils, are capable of operating as an evaporator and as a condenser. A heat pump system typically includes two heat pump heat exchangers, one located outdoor and the other indoor. When the heat pump system is in cooling mode, the indoor heat pump heat exchanger operates in evaporator mode and the outdoor heat pump heat exchanger operates in condenser mode. When the heat pump system is in heating mode, the indoor heat pump heat exchanger operates in condenser mode and the outdoor heat pump coil operates in evaporator mode.
To meet the demands of residential and commercial applications, the size of the core of the heat pump heat exchanger needed to be increased accordingly, which in turn dramatically increased the lengths of the inlet and outlet manifolds. For a heat pump heat exchanger operating in evaporator mode, the increased length of the manifolds tends to result in refrigerant mal-distribution through the row of refrigerant tubes. The effects of momentum and gravity, due to the large mass differences between the liquid and gas phases, can result in separation of the phases in the inlet manifold and cause poor refrigerant distribution through the row of refrigerant tubes. Poor refrigerant distribution degrades evaporator performance and can result in uneven temperature distribution over the core.
To assist in providing uniform refrigerant distribution through the refrigerant tubes, it is known to dispose an inlet distributor tube within the inlet manifold for distributing the two-phase refrigerant throughout the length of the inlet manifold. The distributor tube extends along substantially the length of the inlet manifold and includes a plurality of substantially evenly spaced orifices for evening distributing a liquid refrigerant to the inlets of the refrigerant tubes. Similarly, an outlet collector tube is disposed within the outlet manifold for evenly collecting the vapor refrigerant exiting the outlet ends of the refrigerant tubes.
The outlet collector and distributor tubes are costly in terms of materials, manufacturing, and shipping of the tubes, as well as the time and labor required for the assembling of the tubes in the outlet and inlet manifolds, respectively. Accordingly, there remains a need for a heat pump heat exchanger having a refrigerant distribution control that eliminates the need for at least one of the outlet collector and distributor tubes.